Stars in the universe | Earth, Solar System and Universe.

The stars are masses of gases, mainly hydrogen and helium, which emit light. They are at very high temperatures. In its interior there are nuclear reactions.
The Sun is a star that we have very, very close. We see the other stars as a very small bright spots, and only at night, because they are at enormous distances from us. They seem to be fixed, keeping the same relative position in the heavens every year. In fact, all these stars are fast moving, but at such distances that their changes in position are only perceived through the centuries.
The number of observable stars with the naked eye from Earth has been estimated at about 8,000, half in each hemisphere. During the night can not see more than 2,000 at the same time, the rest are hidden by atmospheric fog, especially near the horizon, and the pale light of the sky.

Astronomers have calculated that the number of stars in the milky way, the Galaxy that belongs to the Sun, amounts to hundreds of billions.

As our Sun a typical star has a visible surface called the photosphere, an atmosphere full of hot gases and, above them, a more diffuse Crown and a stream of particles called stellar wind. The colder areas of the photosphere, which in the Sun are called sunspots, probably are in other common star. This has been proven in some great upcoming stars using interferometry.

The internal structure of the stars cannot be observed directly, but there are studies that indicate currents of convection and density and temperature increase up to the nucleus, where thermonuclear reactions take place.

The stars are composed mainly of hydrogen and helium, with variable amount of heavier elements.

The star nearest to the Solar system is Alfa Centauro

The individual stars visible in the sky are closer to the Solar system in the milky way, our galaxy. The nearest is Proxima Centauri, one of the components of the triple star Alpha Centauri, which is about 40 billion kilometers from Earth.

It is a three-star system located 4.3 light years from the Earth, which is only visible from the southern hemisphere. The brighter, known as "Alpha Centaur A" has a real brightness of our Sun.
Alpha Centauri, also known as Rigil Kentaurus, is in the constellation of the Centaur. At first glance, Alpha Centauri appears as a single star with an apparent magnitude of - 0.3, which makes it the third brightest star in the southern sky.

When observed through a telescope are cautioned that the two brightest stars, Alpha Centauri A and B have apparent magnitudes of - 0.01 and 1.33 and revolve one around the other over a period of 80 years.

The weaker star, Alpha Centauri C, has an apparent magnitude 11.05 and tour around their peers during a period of approximately one million years. Alpha Centauri C also receives the name of Proxima Centauri, which is the nearest to the Solar System star.

Translation for educational purposes authorized by: Astronomía: Tierra, Sistema Solar y Universo